Phased array antenna systems typically utilize narrow band antenna elements that are independently excited by a phased feed system. The phased feed system provides a phase coherent distribution of power, whereby the supplied signal power is delivered to each of the antenna elements in phase. By delivering the power to each of the antenna elements in phase, additive reinforcement of the power of each of the transmitted signals is achieved which is needed for additive antenna gain multiplication. As such, phased array antennas create a directional energy pattern that is useful for various applications, such as radar systems. Thus, as long as the phased feed system provides a phase coherent distribution of power to each of the antenna elements of the array, the power of each of the signals transmitted by the antenna elements is summed together, increasing the signal strength of the antenna in a specific direction.
To provide such phase coherent power distribution to the antenna elements, the coaxial feed lines, or waveguides, comprising the phased feed system are required to be physically cut to a length that is a multiple of the wavelength of the signal to be transmitted. Unfortunately with such a system, as the operating or transmitting frequency of the antenna system is changed, the antenna elements no longer transmit phase coherent signals. As a result, the antenna array transmits signals that are skewed or which points in an undesirable direction. To restore the phase coherent operation to the antenna elements, the feed lines or waveguides are required to be re-cut to a new length corresponding to the wavelength of the new operating frequency, such a step is cumbersome, time consuming and unwanted.
Therefore, there is a need for a wide band biconical antenna that utilizes multiple antenna elements that are aligned about a common axis. In addition, there is a need in the art for a wide band biconical antenna that provides multiple antenna elements that are coupled to a signal source by feed lines that each have the same physical length. Furthermore, there is a need for a wide band biconical antenna that transmits a phase coherent signal independent of the excitation signal frequency. And there is a need for a wide band biconical antenna that provides a helical feed system that minimizes far-field radiation pattern interference during multiple antenna element excitation. Still yet, there is a need for a wide band biconical antenna that provides a helical feed system that maintains a translucent aperture with minimum blockage to the field of view of the antenna.